Project Summary/Abstract The control of RNA Polymerase elongation and termination is not fully understood. In this work, we will investigate the role of the C-terminal domain phosphatases Rtr1 and Ssu72 in the regulation of RNA Polymerase II (RNAPII) elongation and termination. Our preliminary findings suggest that deletion of Rtr1 results in global changes in the efficiency of early termination of RNAPII during transcription elongation. Previous work has shown that disruption of Ssu72 function leads to decreased RNAPII termination resulting in terminator read-through defects. In this proposal, we will test how perturbations of each phosphatase effect transcription elongation and termination. Additionally, we will perform enzymatic characterization of Rtr1 and Ssu72 substrate specificity to further characterize their mechanisms of action. Finally, we will determine the degree of interplay between Rtr1 and Ssu72 to determine if they are able to target unique and/or overlapping sites within the RNAPII C-termination domain. Overall, these studies will shed light on the fundamental process of RNAPII transcription control which is disrupted in numerous disease states in humans.